A manifestation of coronary artery disease is the build-up of plaque on the inner walls of the coronary arteries, which causes narrowing or complete closure of these arteries, resulting in insufficient blood flow to the heart. A variety of techniques have been developed for treating coronary artery disease. Where surgical intervention is necessary, stenoses of the coronary arteries can often be treated using endovascular techniques such as balloon angioplasty, atherectomy, stent placement and the like.
In cases where endovascular approaches are unsuitable or unsuccessful, coronary artery bypass graft procedures typically have been performed using open surgical techniques. Such procedures require an access technique known as median sternotomy, in which the patient's sternum is divided longitudinally and the chest spread to provide access to the heart. The patient's heart is arrested using cardioplegic agents and the patient is thereafter supported by a cardiopulmonary bypass system. A source of arterial blood is then connected to the coronary artery downstream from the target stenotic portion. The arterial blood source may be a venous or arterial graft vessel connected between an arterial source such as the aorta and the coronary artery. Another common arterial blood source is the left or right internal mammary artery which may be grafted to the coronary artery downstream of the stenosis or occlusion.
For a mammary arterial graft to be used in a coronary artery bypass procedure, blood flow through the target mammary artery must be temporarily stopped. Thus, in conventional open chest procedures, a clamp is applied, typically by hand or with forceps, directly to the mammary artery at a position downstream from the patient's aorta. After the mammary artery is clamped, it is ligated and divided at a location downstream from the clamp to create a free end which may be connected to the coronary artery. After completion of the grafting procedure, the clamp is removed by the surgeon by hand or with open forceps to permit blood flow through the mammary artery and into the coronary artery downstream of the blockage.
There are risks and difficulties associated with undergoing a procedure as described above. For instance, stopping the heart beat using cardioplegic agents and placing the patient on a cardiopulmonary bypass system is highly traumatic to the patient and often result in post-operative complications. As an alternative to the foregoing, there are approaches whereby the heart remains beating throughout the entire procedure. In addition, advances have been made in minimally invasive techniques to perform this procedure without opening the sternum, such as the thoracoscopic method described in U.S. Pat. No. 5,452,733 to Sterman, et al., the entirety of which is hereby incorporated by reference.
Another problem with conventional techniques is that blood flowing into the anastomosis site during the grafting portion of the procedure obstructs the surgeon's view of the critical suture placement of the anastomosis. Several devices and methods have been developed to limit or prevent blood loss through and into this anastomosis site. One method is to occlude the diseased target coronary artery with a suture, clamp or other occluding device both distal and proximal of the anastomosis site. The occlusion prevents blood flow into the anastomosis site both from retrograde and antegrade approaches. Dual balloon catheters, such as described in U.S. Pat. Nos. 4,520,823 and 4,404,971 to LeVeen, et al., are useful in obturating blood flow on both sides of a wound, or the site of a surgically detached aneurysm, while the wound is repaired.
Another approach is to direct a CO.sub.2 jet at the anastomosis site during the procedure. This technique blows the blood out of the surgical site; however, it can result in injury to the targeted coronary artery, causing the endothelial layer of the vessel to be stripped away due to the force of the air jet.
Other improvements provide blood flow distal, or downstream, of the anastomosis site during the procedure. Occluding the anastomosis site by distal (single balloon) or distal and proximal (dual balloon) means without such perfusion can lead to myocardial ischemia and potential damage to the very heart muscle that the surgeon is trying to re-perfuse.
U.S. Pat. No. 4,230,119 to Blum discloses a micro-hemostat consisting of a bar that is inserted into a blood vessel by incision and whose ends are then inflated to occlude blood flow immediately adjacent the wound. The bar, however, forms a tube through which blood may flow during the procedure.
U.S. Pat. No. 5,106,363 to Nobuyoshi, the entirety of which is hereby incorporated by reference, discloses a conventional single balloon/dual lumen dilation catheter for use in dilating stenoses to improve blood through coronary arteries. This device utilizes a pump that delivers the patient's own blood from an intake in the catheter disposed in the patient's bloodstream proximal of the treatment site. The patient's blood is pumped through the outer sheath, then conducted to and through the inner lumen of the catheter, finally exiting into the patient's bloodstream. This device obviates the need for making an additional incision for blood intake, and also perfuses blood distal to the treatment site.
U.S. Pat. No. 4,581,017 to Sahota discloses a balloon perfusion dilation catheter which consists of holes located proximal and distal of the balloon so that when placed in a blood vessel, blood may flow to the vessel downstream of the occluded treatment site.
Likewise, U.S. Pat. No. 4,771,777 to Horzewski et al. describes a similar dual balloon perfusion catheter that can be used in conjunction with a pump to perfuse the patient's own blood to a region distal of the site being treated by the second dilatation balloon. The first balloon is used to form a blood seal between the catheter and a guiding catheter.